1. Field of the Invention
This invention relates generally to a seal for rock bits, and more particularly to improved seal and seal shield assemblies for retaining lubricant within the bearing area of a bit and sealing the bearings of the bit from abrasive materials in the borehole.
2. Brief Description of the Prior Art
Seal assemblies for use in applications involving a sliding, rotating or static journal member in a sleeve housing are in common use. As the seal assemblies often function in dynamic circumstances with differential pressure applied to the assemblies much effort has been directed to development and improvement of seal assemblies. The invention disclosed is applicable to the rotary cone rock bit but may be used in a variety of industrial applications.
Rotary cone rock bits in commercial use typically consist of a main bit body with multiple legs. Each leg supports a roller cone cutter on a bearing journal protruding from the leg. The cutter is typically maintained in position on the journal by a thrust-loaded ball bearing assembly. The annular space between the cutter cone and the bearing journal is filled with lubricant. Longevity of the rock bit assembly depends on maintaining appropriate clearance between the cutter cone bearing and bearing journal, and maintaining lubrication, which, in turn, is dependent on the seal assembly.
Roller cone rock bits have an axial opening through the main bit body for circulating drilling mud to wash the debris from drilling out through the bore hole. The seal assembly shields the bearing from contamination by the debris and retains the lubricant between the journal and cutter.
Problems are commonly encountered with sealed drilling bits in the following areas:
a. The destruction of the elastomer seal caused by the drill bit heating up and the elastomer seal adhering to the contacted steel members.
b. Abrasives and sharp particles contacting and thus cutting and abrading the seal, with further migration into the bearing, resulting in abrasion of the bearing and in the escape of lubrication.
c. Differential pressures on the seal assembly distorting the seal and allowing leakage.
d. Chemical decomposition of elastomer seal materials resulting from hydrogen sulfide, steam and other adverse substances encountered down hole.